Kerguelen Plateau-Broken Ridge: A Large Igneous Province (ODP Leg 183 Safety Report)
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Leg 183 will penetrate igneous basement to depths of-200m at several morphologically and tectonically diverse locations on the Kerguelen Plateau-Broken Ridge Large Igneous Province (LIP) in Southeastern Indian Ocean. This leg will build on results obtained by basement drilling at four ODP sites on the Central and Southern Kerguelen Plateau during Legs 119 and 120. LIPs are important to understand because the very large ·amounts of magma entering the crust in a relatively short time interval reflects mantle processes that differ from those causing magmatism at diverging and converging plate margins; for example, LIPs may result from decompression melting of a mantle plume. A major objective of this leg is to infer eruption rates (km3/yr) by determining the eruption ages of the uppermost igneous crust at several locations. Additional goals are to determine the mechanism of plateau growth and the tectonic history of the plateau by integrating seismic data with studies of the sedimentary and igneous cores. Specifically, these cores will be used to address the following issues: the timing and extent of initial uplift; the relative roles of subaerial and submarine volcanism; the cooling and subsidence into a submarine environment; and the multiple episodes of post emplacement deformation. A unique aspect of this LIP is its clear association with a long hot-spot track that formed from -82 to 38 Ma (i.e., the Ninetyeast Ridge with seven DSDP and ODP drill holes that penetrated igneous basement), and the Kerguelen Archipelago and Heard Island which have a volcanic record from -40 Ma to the present. Studies of the subaerial lavas from these islands and submarine lavas recovered by drilling provide a 115 Ma record of volcanism that can be used to understand the origin and evolution of the large and long-lived Kerguelen plume. This plume is particularly important because it is a source of the "enriched isotopic component" which forms an end-member in the isotopic arrays defined by ocean island basalts, and it may have been important in creating the distinctive isotopic characteristics of Indian Ocean ridge basalts. Determination of the spatial and temporal variations in geochemical characteristics of the basalts forming the Kerguelen Plateau and Broken Ridge are essential for understanding the early history of the Kerguelen Plume.